1. Technical Field
The present invention relates to a data recording device, and, in particular, to an improved method and system for controlling the movement of a read/write head of a data recording device. Still more particularly, the present invention relates to an improved method and system for controlling the movement of a read/write head of a data recording device, wherein an initial value compensation method is selectable for determining a control signal for controlling the movement of the read/write head.
2. Description of the Related Art
A data recording device, such as a hard disk drive device or an opticalmagnetic disk drive device, is utilized for writing the data in a data recording track and reading data from the data recording track. For a hard disk drive device, one end of the arm is pivotally supported on a frame of the hard disk drive device, and the read/write head is mounted on the other end of the arm. The arm is moved to a target data recording track along the radius direction of a magnetic recording disk by an actuator to perform the read/write operation.
A control scheme has been implemented which shortens a time period for moving the read/write head from a current position or a start position to a target position or a target track position and precisely positions the read/write head on the target track to improve performance of the hard disk drive device. To this end, a control scheme has been utilized, which utilizes a combination of multiple operation modes during a positioning period for moving the read/write head from the start position to the target track position.
With reference to FIG. 1, there is depicted a timing diagram representing operation of the positioning period for moving the read/write head from the start position to the target position. A curve 1 illustrates a trace of the read/write head moved in this control scheme. A curve 2 depicts a trace of the read/write head moved in the case that the IVC method, later described, is utilized.
A selective combination of a seek mode operation, a settling mode operation and a following mode operation is utilized in the positioning period in accordance with a distance between the start position of the read/write head and the position of the target track. In particular, in the case that the distance between the start position and the target position is long, the seek mode operation, the settling mode operation and the following mode operation are performed.
In the seek mode operation, a target speed of the read/write head, in accordance with the distance between the start position and the target position, is selected. In addition, a speed control for bringing the speed of the read/write head to the target speed is performed. When a position/speed control device detects at a sampling time "n6" that the read/write head has reached a position which is separated from the target position by a predetermined distance L1, i.e. a predetermined number of remaining tracks, the position/speed control device switches the operation mode from the seek mode to the settling mode.
In the settling mode, the moving speed of the read/write head is increased and decreased. When the position/speed control device detects at a sampling time "n15" that the read/write head reaches a position which is separated from the target position by a predetermined distance L2, the position/speed control device switches the operation mode from the settling mode to the following mode.
In the following mode, the moving speed of the read/write head is increased and decreased to position the read/write head on the target track. Further, after the following mode, the position/speed control device performs an operation mode for maintaining the read/write head on the target track.
Referring now to FIG. 2, there is illustrated a block diagram of a feedback loop of the position/speed control device and a mechanical system, i.e. the actuator and the arm, in the case that an initial value compensation (IVC) method is not utilized. State variables Xp(n) of the mechanical system at the "nth" sampling time are depicted in FIG. 2. In particular, since an effect of higher terms such as y(n-2), . . . , U(n-3) is small, these are omitted. ##EQU1##
The sampling times in the case that the IVC method is utilized are depicted in FIG. 1. At each of the sampling times, the start position of the read/write head is detected. The "y(n)" represents a positional deviation signal=(the current position of the read/write head--the target position) at the sampling time "n". Usually, the target position is represented by "0". For example, if the read/write head is positioned at a position separated from the target position by 300 tracks, the value of y(n) is 300, in other words, the value of the positional deviation signal is 300. "Y(n-1)" represents the positional deviation signal at the sampling time "n-1". "U(n-1)" represents the output signal of the position/speed control device generated at the sampling time "n-1". This output signal is stored in the position/speed control device. "U(n-2)" represents the output signal of the position/speed control device generated at the sampling time "n-2". This output signal is also stored in the position/speed control device.
The position/speed control device generates the output signal U(n)=kXc(n) at each of the sampling times, and supplies the output signals to the actuator, i.e. a voice coil motor, as depicted in FIG. 2. A value "k" is a vector, and the value of "k" is changed in accordance with the operation mode. More particularly, a vector "km" is utilized in the seek mode, a vector "ks" is utilized in the settling mode, and a vector "kf" is utilized in the following mode, the operation of each operation mode is controlled by the value of "k". It is noted that the state variables Xp(n) of the mechanical system, i.e. the actuator and the arm, are substantially equal to the state variables Xc(n) which are utilized by the position/speed control device, as illustrated in FIG. 2. Although Xp(n) is not actually equal to Xc(n) since Xp(n) includes higher terms, it can be considered in controlling the mechanical system of the hard disk drive device that Xp(n)=Xc(n).
The operation for switching the operation mode from one mode to another mode is a discontinuous operation. More particularly, even if each of the operation modes is optimized, an entire positioning operation including the combination of these operation modes does not become an optimized operation. To solve this problem, an initial value compensation (IVC) method has been proposed. As described, curve 2 in FIG. 1 illustrates the trace of the read/write head moved in the IVC. Along curve 2, the state at the time point or the sampling time "n0" at which the operation mode is switched from one operation mode, such as the seek mode, to the succeeding operation mode, such as the settling mode, is treated as the initial state of the settling mode. At the switching time "n0", the state variables or parameters utilized by the position/velocity control device for controlling the settling mode are set to new state variables Xc(0)'=KXp(0)=KXc(0), wherein K is a matrix.
Various proposals for calculating the new state variables Xc(0)'=KXp(0)=KXc(0) have been made. For example, in U.S. Pat. No. 5,164,931, Xp(0) is calculated by utilizing the distance to the target track and the speed as the state variables. In U.S. Pat. No. 5,561,568, Xp(0) is calculated by utilizing position signals of the read/write head, P(0), P(-1), . . . , and signals U(-1), U(-2), . . . , to the actuator/arm as the state variables. By the IVC method in these patents, the new state variables Xc(0)'=KXp(0) are calculated only at the transition from the switching time to the settling mode, and the output signals required in the settling mode are generated based upon the new initial value. In the settling mode utilizing the IVC method, a rapid acceleration or speed up, and a rapid deceleration or speed down of the read/write head are performed in comparison with the case without utilizing the IVC method, so that the time period for positioning the read/write head can be shortened, as depicted in FIG. 1.
Although the time period for positioning the read/write head to the target track can be shortened by utilizing the IVC method, the following problems typically arise. A first problem is that, in the case that the rapid speed up and the rapid speed down of the read/write head are required at the switching time from the seek mode to the settling mode, the position/speed control device generates a pulse output signal of a large amplitude including high frequency components. Thereby, the length of the settling period is extended due to the high frequency components of the pulse output signal. More particularly, the high frequency components cause the mechanical vibration of the actuator, the arm and the read/write head to generate, and the length of the time period for completing the settling mode is extended due to the mechanical vibration. In other words, the use of the IVC method extends the time period of the settling mode, so that the total time period for positioning the read/write head is extended in comparison with the settling mode without utilizing the IVC method.
A second problem is that, in the case that the IVC method is utilized, a time period for calculating new state variables Xc(0)'=KXp(0) is required at the switching time from the seek mode to the settling mode, and the generation of the control signal of the settling mode is delayed by this calculation time period. To solve this problem, in IBM Technical Disclosure Bulletin, Vol.39, No.11, November 1996, p.p.95-98, a value of Xc(0)' corresponding to a moving distance of the read/write head and the output U(0) of the control device at the switching time are stored in a table. In the case of the hard disk drive device with the disk having more than 10,000 data tracks, a vast table is required to store the data, so that this scheme can not be utilized in practical products.
Therefore, in view of the foregoing, it is desirable to provide a data recording device and method for controlling the data recording device which solves the various problems caused in the case of utilizing the IVC method.